Read the text and answer questions 10 to 12

    My favourite thing is aquarium. It is a place in which aquatic plants and animals, particularly fish, are kept. The term is applied to single tanks for home use in which fish are kept for their decorative effect and interesting habits and to public institutions with tanks for exhibition and scientific study of aquatic life.

    I make home aquariums to simulate a natural environment. Aquatic plants supply the oxygen needed by the fish, but often an aerating device is used to furnish additional oxygen. Goldfish enjoy cool water, but the popular tropical fish must have water at a constant temperature of 22°C (72°F) or more. I must keep the water pure and free of algae for long periods by sufficient aeration and by keeping mollusks in the aquarium. A layer of sand or gravel at the bottom of the tank will hold the roots of such important aquatic plants as tape grass, vallisneria spiralis, and aid in the removal of debris. My home aquariums range in size from small fishbowls holding two or three pets to huge tanks.

10.  To give additional oxygen, ... is used in a home aquarium.